The comedy-sketch show, which has been made at a cost of up to €1m, according to a well-placed RTE source, has gained just a 21pc share of the audience on Sunday nights, nearly one-third below the average for that slot of 31pc.

The prime-time entertainment broadcast lost more than 35,000 viewers after its first episode.

Critic Liam Fay panned it as a "smug farrago".

Irish Independent reviewer John Boland wrote: "By my count, there were 17 sketches in Sunday night's opening show, and I managed a faint smile at just two of them."

Speaking to the Sunday Independent this weekend, an RTE spokesperson said it was unfair to compare the show to the hugely ­popular Love/Hate, which was a ­broadcasting phenomenon.

That's a fair defence but Mario's offering is also ­performing worse than his main rival in mimicry.

Callan's Kicks, featuring ­Oliver Callan, opened with 32pc audience share and more than 400,000 viewers in the difficult summer season last year, while Mrs Brown's Boys has never fallen below 30pc, even on a repeat night.

However, RTE pointed to another show, Irish Pictorial Weekly, to stress that a drop of 35,0000 viewers is not ­unusual for the broadcaster. Irish ­Pictorial Weekly dropped 90,000 after one night on air.

This weekend, a Montrose source said the Gift Grub ­creator will be feeling the hit from the poor ratings: "A lot more was expected for this show as RTE has spent a ­fortune on it and it should at least get 30pc of the available audience on a Sunday night, where the audience is ­captive. The way it's going he will have less than half the average ­audience and below 300,000 before long."

TV critic Fay pointed to what he called "bum writing" and some unconvincing impressions.

"One hour is way too long for an impressions show, and the reliance on slapdash filler is unignorable," the review stated.

Meanwhile, Callan's Kicks is awaiting a second series but RTE chiefs are nervous about its sharper, more biting tone in comparison to the lighter feel of Mario, especially approaching the year of a general election.

Callan's close-to-the-bone sketches include President Michael D Higgin's working relationship with his assistant Kevin McCarthy (which RTE asked the comic to tone down) and his infamous portrayal of former Taoiseach Brian Cowen.

A well-placed source told the Sunday Independent: "This is the most high-profile slot you can give comedy and the audience is so huge it's almost impossible not to do well.

"But Mario's show just isn't funny and viewers are voting with their TV remotes."

The source added: "Dressing up as Marty Morrissey or Joan Burton is not enough. The writing was hit-and-miss but it is early days and no-one can deny that Mario is extremely talented. We were a little surprised he's still doing Miriam after overusing her for two previous series. He doesn't have the content to do the show every Sunday.

"The production values of the show are worryingly low too, give the size of the budget available.

"Mario doesn't appear to want to move the show on from last time. He's doing the same routine. It hasn't worked, so far."

RTE were keen to point out that Rosenstock is up against serious competition on Sunday nights.

"It's a very tough slot," taking on I'm a Celebrity . . . Get Me Out of Here! on UTV Ireland, said the RTE spokesman.

Speaking about the cost of Mario's show, a spokesperson for the broadcaster said: "RTE will not be in a position to confirm the budget for the show as this information is commercially sensitive."

Asked if the station was tied into a two-year TV contract with the star, the spokesperson added: "We do not comment on the individual contracts of our talent."